This invention is directed to a process for reducing the sulfur and ash contents of coal.
The United States, with nearly one-half trillion metric tons of coal reserves, has the largest total coal reserves in the world. Increased coal utilization in this country has been hampered by environmental constraints, such as restrictions on sulfur dioxide, nitrogen oxides, and particulate emissions. There is a need for new technology to meet these environmental constraints at costs acceptable to coal users.
Molten caustic can be used to leach ash and sulfur from coals as described in aforementioned U.S. Pat. No. 4,545,891. Difficulty is incurred in recycling the caustic used in the process. Costly environmental considerations dictate reuse, rather than disposal, of the spent caustic.
Before mentioned Application Ser. No. 770,324 describes a process by Meyers et al. that allows for reuse of the caustic. In this process, the coal is sequentially treated with fused alkali metal caustic, water, carbonic acid, and a strong acid such as sulfuric acid. Although this process allows recovery and reuse of the caustic, it requires two acid-treating steps, which adds to the cost of the process, and necessitates storage of two different acids.
Accordingly, there is a need for a process using molten caustic that can effectively remove sulfur and mineral matter from coal, and enables the caustic and acid solutions to be recovered for reuse in the process, without requiring the use of two different types of acids.